Thermal hazard risk and decomposition mechanism identification of nitrobenzene with mononitrophenol impurities: Combined kinetic and products analysis

Nitrobenzene (NB), as a critical chemical intermediate with annual consumption exceeding one million tons, is widely used in the chemical manufacturing industry. However, its poor thermal stability when contaminated with impurities has caused multiple fire and explosion incidents. This study aims to investigate the effects of two typical phenols, p-nitrophenol (PNP) and o-nitrophenol (ONP), on the thermal behaviors of NB, and elucidate the impact mechanism. Experimental results indicate that the addition of 10 % wt. PNP or ONP significantly reduces the main decomposition peak temperature of NB, initiating low-temperature exothermic reactions. Kinetic analysis reveals that while these additives increase the activation energy, the dramatic rise in pre-exponential factor indicates fundamental changes in the decomposition pathway. Specifically, NB-ONP exhibits the highest apparent activation energy due to intramolecular hydrogen bonding. Cleavage of these hydrogen bonds generates highly reactive phenoxy radicals that drive an efficient nitro-reduction pathway, leading to the most pronounced thermal hazard. Pure NB decomposition follows a second-order reaction model (F2), while mixtures with PNP or ONP conform to nucleation-growth (A3) and first-order (F1) models, respectively. Product analysis confirms that phenolic impurities reconstruct the reaction network through more complex pathways. Consequently, the thermal hazard risk follows NB-ONP > NB-PNP > NB. These findings provide crucial guidance for NB production: priority should be given to controlling high-risk ONP impurity generation by optimizing nitration process conditions to suppress relevant side reactions. The study clarifies the microscopic mechanism and provides important theoretical basis for targeted impurity management and safe NB production.